First aim is to obtain better insight into hemopoietic proliferation particularly granulocytopoiesis, and its regulation in health and in blood diseases. Second is development of a method to determine the sensitivity of acute leukemia (AML) cells to chemotherapeutic agents to preselect the most effective drug(s) for therapy. The studies use diffusion chamber (DC) cultures and other in vitro culture systems. Tissue cultures are used, since in vivo study of cell proliferation with radioactive precursors of DNA can only be used in man to a very limited extent. Non-T, non-B, non-phagocytic, unidensity, mononuclear cells will be obtained from human blood and marrow. These cells will be cultured in DC's in irradiated and non-irradiated hosts and with the addition of "pure" populations of monocytes and neutrophils to study the cellular and humoral factors influencing the proliferation and differentiation of stem cells. The stem cell concentration in blood and marrow will be determined in DC's by limiting dilution technique. Single cells will be cultured in the DC's, agar DC's (ADC's) and in vitro soft agar dishes to determine morphology, potency to produce diverse cell lines and the number of cells produced per stem cell. Efforts will be made to show existence of and characterize "pluricellpoietin" an assumed regulator of stem cell proliferation. Human AL cells will be cultured in DC's, ADC's, and double diffusion chambers to see if they mature in non-leukemic environment, mixed with normal marrow cells, to see if they suppress normal stem cell differentiation, and if AML cells produce a factor that suppresses normal granulopoiesis. AML cells will be exposed to PHA and then subcultured in DC to develop a system of rapid growth in which it may be practical to assay the effectiveness of chemotherapeutic agents and preselect drugs for leukemia therapy. Peritoneal lavage studies in dogs will be continued to separate the leukocytosis inducing factor and colony stimulating factor by column chromatography. The purified forms of these factors will be tested in dogs to evaluate their in vivo role as regulators of granulocytopoiesis.